Background. Firefighting requires tremendous cognitive demands including assessing emergency scenes, executing critical decisions, and situational awareness of their surroundings. The aim of this study was to determine the effects of differing rates of increasing core temperature on cognitive function during exercise-induced heat stress. Methods. Nineteen male firefighters were exposed to repeated cognitive assessments, randomized and counter-balanced, in 30°C and 35°C and 50% humidity.

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... % humidity. Participants performed treadmill walking (4.5 km.h-1 and 2.5% grade) with cognitive function assessed before exercise (PRE), after mounting the treadmill (Cog 1), at core temperatures of 37.8°C (Cog 2), 38.5°C (Cog 3), and 39.0°C (Cog 4), after dismounting the treadmill (POST), and following an active cooling recovery to a core temperature of 37.8°C (REC). The cognitive tests implemented at PRE and POST were spatial working memory (SWM), rapid visual information processing (RVP), and reaction time (RTI) while paired associates learning (PAL) and spatial span (SSP) were assessed at Cog 1, Cog 2, Cog 3, and Cog 4. All five cognitive tests were assessed at REC. Results. Planned contrasts revealed that SSP and PAL were impaired at Cog 3, with SSP also impaired at Cog 4 compared to Cog 1. REC revealed no difference compared to Cog 1, but increased errors compared to Cog 2 for PAL. Conclusions. The decrements in cognitive function observed at a core temperature of 38.5°C are likely attributed to the cognitive resources required to maintain performance being overloaded due to increasing task complexity and external stimuli from exercise-induced heat stress. The addition of an active cooling recovery restored cognitive function to initial levels.